A communication satellite makes possible the existence of large networks of communication equipment that can span a wide geographical area. One type of satellite communication system is a point to multipoint configuration wherein equipment at a single location, termed the uplink, may send data, control information, audio and video signals to hundreds or even thousands of individual locations, called downlinks. The downlinks are receiving stations and may be geographically positioned over the entire country or any other geographic area. The data and signals from the uplink are transmitted via satellite to the downlinks virtually immediately. These point to multipoint communications networks have a variety of uses such as simultaneously switching audio and video programming as in a cable television network, sending electronic mail, or controlling equipment at physically remote outposts, as well as many other applications.
Some point to multipoint systems, once established, are inflexible and cannot accommodate new equipment types without modification to the arrangement of data and control signals. Also, some systems are intolerant to transmission errors and are susceptible to giving the wrong information or output when an error occurs. Another difficulty with some systems is the inability of the uplink to direct commands to a set of the remote downlinks other than all of the downlinks. It will be appreciated that it will be highly desirable for the uplink to direct a command to an individual downlink.
In addition, there are various simple and tiered schemes for grouping the downlinks. Most of these schemes, however, rely upon the uplink to remember the group membership and simply broadcast a list of individual identifiers with a command when group addressing is desired. Accordingly, it will be appreciated that it would be highly desirable to have an addressable system wherein the downlinks only respond to data intended for them.